GB 2 407 042 A discloses an inhaler with a rolled-up blister strip. The inhaler comprises a manually operated, pivotable actuator, which operates a conveyor for stepwise moving the blister strip. The actuator supports a piercer and an associated mouthpiece. By pivoting the actuator, the blister strip and be moved forward and blister pockets of the blister strip can be pierced one after the other. When a patient breathes in an air stream passes through the previously pierced blister pocket, with the result that the inhalation formulation in the blister pocket mixes with the air and is discharged to the patient.
The present invention relates to passive inhalers, i.e. inhalers where the patient or user breathes in to generate an air stream, which entrains the inhalation formulation and forms the desired aerosol.
When a patient puts a mouthpiece or any other end piece in his mouth and breathes in, an air stream is sucked through the inhaler to generate the aerosol and to discharge the inhalation formulation as aerosol. A pressure drop occurs within the inhaler when the air stream flows through the inhaler. This pressure drop depends on the flow per time and flow velocity. The flow resistance represents a quantity relating to the square root of the pressure drop at a certain flow rate.
In the present invention, the term “flow resistance” means the resistance which occurs when air is sucked from the mouthpiece or any other end piece of the inhaler during inhalation, i.e. with generation of an aerosol of the inhalation formulation.
The design of a piercing member for puncturing the blister pockets is important in order to achieve good discharge characteristics. Multiple piercing member designs are known, e.g. from FR 2 881 111 A1, GB 2 407 042 A, WO 2004/103446 A1, WO 02/094357 A1, GB 2 375 309 A, WO 01/26720 A, WO 99/062495 A, WO 99/47099 A, DE 197 57 208 A1, WO 97/40876 A, and WO 96/09085 A.